The present invention relates to motor controllers and more specifically to a method and apparatus for driving an inverter where the frequency and magnitude of AC output voltages to a load are independently controllable.
There are several different standard inverter control modes that are known in the industry including a volts per hertz (V/Hz) mode and a vector control mode. In the V/Hz mode, during regular modulation, inverter output voltage/frequency linearity is achieved by maintaining a constant voltage/frequency ratio over a linear operating region. When operating during overmodulation (e.g., non-linear region of operation), control is compensated for lost voltage so that the voltage output profile remains linear.
While V/Hz and vector control modes of operation are well suited to driving three phase loads such as motors, unfortunately these modes are not well suited to driving other load types where variable voltage at a fixed frequency or variable frequency at a fixed voltage may be desired such as, for instance, in systems provided to power linear motors, vibration welders, induction heaters, power supplies, vibratory feeders/conveyors, electromagnetic stirrers, resistive loads and other non-motor load applications.